When Cortana regained full systems control, it was too late to stop the ship from crashing into the Moon. A new six mile crater appeared on the pocketed surface of the moon as the Pillar of Autumn II crashed into its surface. She found it strange that the ship didn't become embedded in the moon, since it had crashed bow-first.
The ship was damaged beyond repair. The fusion reactors were scrap metal, cracked open by the blast from the Forerunner ship. The nuclear start-up reactor was intact, for all the good it did. One of the Super MAC cannons was offline, but good news was the plasma turrets were still functioning.
Cortana rebooted the tracking system, only to discover that hundreds of Droid boarding craft were headed for them.
"Admiral Keyes," Cortana reported. "We have multiple boarding craft inbound on the Autumn's position. I advise all marines onboard to defend the ship at all costs."
"Understood," Miranda acknowledged. "Sergeant, send the order through the ship to keep the Droid Army from taking it."
"Yes ma'am," Johnson said, and saluted.
Cortana returned to her analysis of the moon's surface. It was made of granite, but upon closer examination, Cortana found an unknown metal substance in a crater one mile due north of their position. She triple-checked her calculations. There was no error.
There was a Forerunner complex inside the Moon itself.

Ghazghkull watched as the Droid Army fleet withdrew from the battle and proceeded to the moon orbiting Earth. He turned to Zagdakka.
"Ready the Assault boats," Ghazghkull ordered, "I will be personally leading this operation. Send a message to the other Ork Warlords to get to my ship. There's another battle to be fought."

Sergeant Johnson fired his Sniper Rifle, and blew the head off a Droid Commander that had just exited a boarding craft, adding it to the headless tin can to the pile of Battle Droids in the doorway.
The Battle Droids had captured the engine room, and had been attempting to capture the armoury that Johnson had been inside, gathering weapons for the bridge crew. A squadron of Marines had been there at the same time, and now three were left. The Battle Droids paused about an hour ago, and had started again five minutes ago.
"Sarge!" Ensign Tolkaze yelled over the sound of gunfire. An Arabian, he was naturally olive in complexion, but looked white as a ghost under his helmet. "We can't hold them off much longer!"
"Damn it, Tolkaze!" Johnson yelled, "We will hold them back, even if they send their best bastards at us! You're a Marine, soldier! Start acting like it!"
A Battle Droid stuck it's head around the corner, then pulled it back as Johnson fired at it. The corridor became deathly quiet.
Suddenly, Durge dropped down from the ceiling vent inside the armoury in his humanoid form. He pulled out a captured Energy Sword and charged Tolkaze.
Tolkaze ducked underneath the blade and planted a Plasma grenade to the breastplate of Durge's armour. He dived through the behemoth's legs as the Plasma grenade exploded.
"That count as acting like a Marine?" Tolkaze asked.
"We'll see," Johnson answered grimly.
As the smoke cleared, Durge turned and faced the Marines in his true form. He lashed out at Tolkaze with his left arm, stretching like rubber, and snapped the poor marine's spine. Johnson could have sworn that he heard Tolkaze mutter, "Praise be to Allah." He grabbed a Shotgun from the rack and fired a shell at the beast.
Durge turned and charged Johnson, grabbing Tolkaze's Battle rifle as a club. Johnson slammed the butt of his gun into Durge's face, causing him to stumble backward. Johnson saw an opening, and picked up a crate of Plasma grenades.
Johnson tossed the crate at the Durge, and followed through with a Frag grenade to detonate the Plasma grenades, yelling, "Frag out!"
The crate landed on Durge's head, while the Frag landed at his feet. Durge moaned, and the Frag blew. The heat set off the Plasma grenades, destroying Durge as his body liquefied, then evaporated in under a second. All that remained of Durge was his helmet. Johnson kicked it into a corner.
Johnson got to his feet, and shouted at one of the marines. "Get Admiral Keyes on the line!"

"Understood, Cortana," Keyes said as Cortana finished outlining the plan. "Sergeant, get your men to the hangars. Once you get there, get a Pelican, and head for a crater one mile north of here on the Moon's surface. We'll meet you there."

Thomas walked to cockpit of the Pelican, listening to the emergency transmission from the Cortana through his Comm. He replayed the message, and put it on speakers. He looked back to get an idea of what 5th platoon thought about this. They all had there helmets on so he couldn't see their facial expressions, but their body language gave them away. They would go. Thomas turned to the Master Chief.
"You sure about this?" Thomas asked over a private channel. "If Cortana is right, and there is a Forerunner installation there, there is a good chance that it's crawling with Sentinels, Enforcers, and who knows what other Forerunner robots they have in there. And we all know that if there are Sentinels, you can be certain there are Flood in that structure. You sure you want to do this?"
"You know the code of conduct, Major," the Master Chief answered. "Never leave a fellow soldier behind."
Thomas nodded, and passed the order to the Pelican's pilot. They were going in.

Nugga turned to his three comrades in the hold of the Phantom.
"Friends," Nugga began, "We were orginally headed for the Moon to rescue the crew of the Pillar of Autumn II, but the circumstances have changed dramactically. The ship's AI discovered a Forerunner structure on the Moon. Now our orders are to recon the installation and elminate any parasite that are not in statis, if there are any Flood at all. Apparently ONI Section Three wants us to get a specimen for them."
"Do you honestly expect us to listen to a bunch of desk workers?" Glor asked politely.
"Of course not." Nugga answered. "If see any Flood, you kill first, ask questions later."
"We here!" The Unggoy pilot shouted fearfully. Nugga nodded to his squad, and the four of them dropped down to the Moon's surface via the grav lift. This will be an interesting recon mission, Nugga thought as he felt the uncanny felling that his stomach was still on the Phantom.

Grievous walked into the bridge of the Pillar of Autumn II, Durge's helmet in his left hand. He encountered no resistance until he reached the navigation terminal. Cortana had been removed from the ship's computer, but that didn't mean Grievous couldn't figure out where they were headed. Grievous had been an elite hacker during the last civil war between the Forerunner, and had cracked the enemy encryption codes, and had led his side to victory. That was how he gotten to this position.
Grievous rebooted the computer terminal, and mentally smiled. The UWSC had a long way to go before their technology even came close to equaling the Forerunners' skill. Grievous typed in a series of symbols, using an alphanumerical hacking code that he was certain even an electronic being as modern as the ship's AI couldn't block, then hit the Enter key. It took three seconds to insert itself in the system, then it recalled the coordinates from the deleted files that had been deleted from the recycle folder. Grievous chuckled. This is child's play. He turned to the Super Battle Droids that had escorted him to the bridge, and led them back to his shuttle.

Ghazghkull walked toward his personal Assault boat, which looked like a kilometer-sized asteroid. The other Warlords were already onboard, ready for the fight. Ghazghkull had received a transmission from Grievous ordering Ghazghkull to come and help him explore the Forerunner installation. Ghazghkull was going, but only because he wanted to. He stepped into the Assault boat. The Assault boat rose a few meters above the deck, and streaked out of the ship and toward the Moon.

Aboard the Cairo, a radar officer noticed an anomaly near the Moon. Three seconds later, High Charity appeared next to the Moon, dwarfed by its size. It landed upturned on the Moon near the recently discovered Forerunner structure.
A Super MAC round from the Gorka and Morka slammed through the MAC platform's Comm array a minute later, obliterating their capability to contact anyone. The Cairo continued firing at the enemy fleet, unable to communicate. The UWSC forces were on their own.